A traditional subsea manifold is a device that is designed to control the flow of fluids from oil wells and direct the flow through various production/injection loops that are made of piping, valves, connector hubs and fittings. A traditional subsea manifold also typically includes various flow meters and controls systems for monitoring the flow of the fluids and controlling various valves. The most common joining method for the piping, valves, hubs and fittings is by welding but bolted flange connections are also used.
The manifolds can be classified into: production (oil, gas or condensate), water injection, lift and mixed (production and water injection). They all have a similar basic structure. A typical subsea manifold has a main base which is a metal structure that supports all piping, hydraulic and electrical lines, production and crossover modules, import and export hubs and control modules of the subsea manifold.
Typically, to design a subsea manifold certain information is needed: a flowchart of fluid flow, the number of Christmas (wells) trees that will be linked, and possibly other platforms manifolds. In general, the flowchart of fluid flow is provided by the client. With the requirements of the system, it is possible to begin the process of designing the elaborate arrangement of pipes, valves and hubs that will be part of the subsea manifold. A typical subsea manifold also includes an arrangement of structural members, e.g., a support structure comprised of beams and cross members that are designed to facilitate the installation of the manifold, distribute external loading and also support the arrangement of pipes and other equipment or components of the subsea manifold.
Below is one example of a summary of the steps for preparing the design of the conventional subsea manifold.
1. Flowchart.
2. Prepare the design of the arrangement of pipes, valves and hubs.
3. Prepare the design of the metal support structure.
The conventional subsea manifold promotes the flow of fluid from the oil and gas wells in manner mandated by the fluid flowchart of the project, through a complex arrangement of numerous flow paths that are defined by welded pipes, pipe fittings, such as elbows and/or flanged connections. Valves are positioned within the pipe flow paths to control the flow of fluid and there is a requirement to open and close these valves at various times.
FIG. 1a is an example of a traditional subsea manifold 20, while FIG. 1b is view of the subsea manifold 20 with various structural members omitted so as to better show the various flow lines, valves and manifolds that are part of a typical subsea manifold 20. As shown in FIG. 1a, the subsea manifold 20 is comprised of a main base 20a and arrangement of structural members 20b. As noted above, the combination of the main base 20a and arrangement of structural members 20b are designed to support the arrangement of the pipes and other equipment or components of the subsea manifold 20. More specifically, the external structure of the manifold provides a space frame that is used for a variety of purposes: 1) to facilitate the lifting and installation of the manifold 2) to protect the valves and pressure piping from dropped objects, 3) to provide structural support for the connection piping between the tree—manifold and the manifold—export piping and 4) to support piping loads whether induced by weight, thermal or vibration, i.e., to absorb substantially all piping loads. With reference to FIG. 1b, the illustrative subsea manifold 20 is designed for receiving fluid from 4 oil wells and it has two headers 21 that are adapted to be coupled to two flow lines. More specifically, the subsea manifold 20 is comprised of four vertically oriented connections 20c (where flow from each of the oil wells will be received) and four vertically oriented hubs 20d on the headers 21 (for providing input and output connections to two flow lines (not shown) that provide fluid to/from the manifold 20). The manifold 20 also includes eight illustrative inlet flow valves 20d (that direct the flow of fluid received from the wells) and two illustrative header valves 20e to control the flow of fluid within the headers 21. The eight inlet flow valves are positioned in four separate valve bodies 20f (valve blocks are sometimes used in lieu of valve bodies), ten illustrative valves/valve actuators and various piping arrangements and loops 20g comprised of welded pipe sections, fittings and flanges. Additionally, from time to time, various operations are performed to clean out the interior of the various piping loops. e.g., a full diameter pig is forced through the piping system. A pig can also be used for inspection of the pipe and other maintenance and inspection operations. Accordingly, the pipe loops and elbows must be sized large enough such that such pigging devices may readily pass through all of the “turns” within the piping system, i.e., the turns within the piping system must have a large enough radius so as to insure that such cleaning devices may readily pass through the turn in the piping system.
In the depicted example, ignoring the main base 20a and arrangement of structural members 20b, the subsea manifold 20 is comprised of twenty four connections, eighteen spool pieces, which require fifty welding processes, six separate valve blocks and eight hubs 20c, 20d. The key point is that, irrespective of exact numbers (which will change depending upon each application), a typical or traditional manifold requires numerous individual components, and it requires that numerous welding procedures and inspection procedures be performed to manufacture such a traditional manifold. In the depicted example, the subsea manifold 20, including the main base 20a and arrangement of structural members 20b, has an overall weight of about 90 tons—about 33 tons of which are comprised of pressure retaining pipe and equipment and about 57 tons of which are comprised of various structural members 20b and the main base 20a. More specifically, a typical prior art subsea manifold may have an overall length of about 8 meters, an overall width of about 7 meters and an overall height of about 7 meters. Thus, in this example, the traditional subsea manifold 20 has a “footprint” of about 56 m2 on the sea floor and occupies about 392 m3 of space. Of course, these dimensions are but examples as the size and weight of such subsea manifolds 20 may vary depending upon the particular application. But the point is, traditional subsea manifolds 20 are very large and heavy and represent a complex arrangement of piping bends and valves to direct the flow of fluid received from the wells as required for the particular project.
The above noted problems with respect to the weight and dimensions of traditional subsea manifolds 20 is only expected in increase in the future due to the increasing number of valves along with Increases in working pressure and subsea depth, resulting in increased weight and dimensions for future subsea manifolds 20. In short, a traditional subsea manifold 20 is a structure that has a large size and weight that is comprised of many parts: pipes, bends, fittings, and hubs, and involves performing numerous welding operations to fabricate, all of which hinder the process of fabrication, transportation and installation. Installation of a subsea manifold is a very expensive and complex task. The manifold must be lifted and installed using cranes designed for the dynamic conditions created by wave, wind and current conditions offshore. The weight of the manifold combined with the dynamic sea conditions requires large installation vessels that are very expensive to operate. Lifting a manifold typically will require an offshore crane with a lifting capacity that is 2× or 2.5× the weight of the manifold due to the dynamic loading and dynamic amplification that results from motion induced by the sea conditions.
In terms of controlling the operations of subsea manifolds, i.e. the opening and closing of various valves, there are several known actuation means employed to actuate the subsea valves used in subsea manifold systems. One system approach relies on manual valves. With a manual valve equipped manifold, valves are operated by divers (in shallow water applications) or a Remotely Operated Vehicle (ROV) (in deep water applications). A drawback manual valve system is the need to deploy a diver to operate manual valves for shallow water manifolds and deploy an ROV for valve operations when required in a manifold installed in deep water. Another valve actuation method relies on direct connection of hydraulic fluid from the surface to the manifold valve actuator—a direct hydraulics actuation system. One drawback of a direct hydraulic actuation system is the distance between the manifold and the hydraulic supply on the surface. This limitation makes a direct hydraulics actuation system unsuited for deep water or long distance “step-outs”. Another example comprises the use of general hydraulic actuators controlled by an electro-hydraulic Subsea Control Module (SCM). Typically, such a control system consists of an undersea control module (SCM) comprised of an electrical control module used to selectively direct fluid via a series of directional control valves to the manifold valve actuator which is desired to be opened or closed through pipe connected between the actuators and the undersea control module. A compensation system composed of pipe connected to a variable volume chamber is required to receive and discharge fluid that is displace during valve opening or closing. The hydraulic fluid used to power the actuator must be delivered to the control system via an umbilical connecting the hydraulic fluid supply from the surface to the undersea control module. The electrical power and signals to the subsea control module (SCM) can be achieved via dedicated and separate electrical umbilical and hydraulic umbilical or alternately the electrical power and signal transmission wiring can be bundled together with the hydraulic fluid transmission piping within a bundled electric—hydraulic umbilical. The electrical power and signal are transmitted from surface power and signal units through the power, signal and hydraulic umbilical to the undersea control module.
One drawback encountered in this technique is the weight and dimensions of the traditional subsea hydraulic valve actuation system, and this problem is only expected to be more problematic in the future with future subsea manifolds having an increased number of valves along with an increase in the working pressure and the operational subsea depth, all of which result in an increase of weight and size of traditional subsea hydraulic valve actuation systems. Another drawback of this system is the number and/or size of electrical and hydraulic umbilicals and the associated seabed installation costs. Yet another drawback of this technique is the extensive time required for piping installation of electro-hydraulic control system between the SCM and manifold valves—which implies an increase in the time it takes to manufacture the manifolds, plus the associated cost with the necessary equipment such as hydraulic actuators, the subsea control module, the electro-hydraulic umbilical and hydraulic power unit.
An alternative to the technique described above, but less frequently used nowadays, is the use of undersea electric actuators. According to this technique, each manifold valve to be remotely controlled has an electric actuator mounted to the manifold valve and is connected to an electrical control system. The electrical control system consists of a power grid in the manifold to supply power and signals to the actuators connected to an umbilical with electrical leads connecting the undersea system to an electric power unit and control unit located on the surface.
An advantage presented by this second technique is the reduction in time required to manufacture the manifold, since the installation of the hydraulic control system in the manifold is not necessary. However, in spite of reducing the system cost by eliminating the cost of the hydraulic umbilical, the surface power unit and the undersea control module, the use of electric valve actuators makes this system much more expensive than the first one, since such electric valve actuators are expensive items of equipment in the market.
Another known alternative consists of a shared actuation system (SAC). Such a shared actuation system consists of the use of a structure located along one side of the manifold with an actuation tool that is displaced by a mechanism to the interface of each valve at the time of their actuation. In this alternative, the manifold contains only manual valves without remote actuation, and the actuation of any manifold valve is accomplished by use of the SAC. The mechanism, which displaces or moves the actuation tool to a desired location above a valve to be actuated, does it through a Cartesian coordinate positioning system that is moved by hydraulic pistons on rails and operated by an electro-hydraulic control system. The position of the actuation tool is checked by position and flow sensors located in the SAC. The actuation tool consists of a device that enables the interface with the valve stem and applies torque through a hydraulic power system. The number of turns applied is verified through the flow-through in the tool. Typically, the electro-hydraulic control system comprises a hydraulic pipe connected to the SAC, an undersea electro-hydraulic control module, a SAC compensation system, an umbilical containing hoses and electrical leads to supply fluid, electrical power and signals, connected to the hydraulic pressure unit on the surface and the electrical and control power unit also located on the surface. The SAC can be installed separately and removed from the manifold for repair if necessary. As it is known by those skilled in the art, this third alternative was used only once in the industry for remote actuation of valves.
A shared actuation system (SAC) may be employed in an attempt to minimize the drawbacks of the techniques described above. However, the costs of the undersea control module, hydraulic umbilical and surface hydraulic power unit are still present. Another drawback presented by the use of ashared actuation system (SAC) consists of the constructive characteristic of the Cartesian positioning of the system, which requires that the equipment has the same dimensions as the plane where the valves are contained. Such a requirement makes the equipment heavy and difficult to be installed and removed in case of failure or maintenance. In addition, the large size of the equipment compromises the integration of shared actuation system with the manifold, making it complex and difficult or almost impossible to promote interchangeability.
Other control systems of undersea devices are described in the prior art. Patent application US 2010042357 discloses a system and method for determining the position of an articulated member relative to a plane, and said system may be adapted for undersea use. Patent application US 2008109108 discloses a control system for a manipulator arm for use in undersea remotely operated vehicles (ROVs). U.S. Pat. No. 6,644,410 discloses a modular control system composed of independent segments for use in undersea equipment, including manifolds. Patent application US 2009050328 discloses a system for undersea installation of insulation on flowlines, connectors and other undersea equipment from a remotely operated vehicle. Patent application EP 1070573 describes a system for the application and monitoring of undersea installations, such as manifolds valves. However, none of the abovementioned documents discloses the subject matter of the present invention, which advantageously solves the drawbacks of the remote actuation systems of undersea valves described by the prior art to date, namely, excess weight and large size of the system, high costs, long manufacture period, and restrictions on the repair and replacement of parts and the equipment itself.
The present application is directed to an improved manifold with a unique block architecture and shared actuator system that may eliminate or at least minimize some of the problems noted above with respect to traditional subsea manifolds.